Exploring TDP-43 aggregation and disaggregation A spectrum of seemingly diverse neurodegenerative disorders is now unified by a common underlying theme: the accumulation of non-amyloid, ubiquitylated TDP-43 inclusions in the central nervous system. These lethal disorders range from amyotrophic lateral sclerosis (ALS) to frontal temporal dementia lobar degeneration with ubiquitin positive inclusions (FTLD-U). A causative role for TDP-43 in ALS pathogenesis has been validated by the isolation of mutations in the TDP-43 gene, which are associated with familial and sporadic forms of ALS. Moreover, a yeast model of TDP-43 proteinopathies has established a direct connection between TDP-43 aggregation and toxicity. However, the mechanistic basis of TDP-43 aggregation and how ALS-associated mutations affect the aggregation process directly remain unclear. Further, whether there are cellular factors that can antagonize or reverse the aggregation process remains unknown. We are particularly interested in how two AAA+ ATPases, Hsp104 and p97, might antagonize or reverse TDP-43 aggregation. Hsp104 solubilizes and reactivates proteins from denatured aggregates. p97 prevents aggregation of model substrates, and mutations in p97 are linked with conditions where TDP-43 forms intranuclear aggregates. We hypothesize that understanding these issues will greatly enhance our understanding of ALS and related disorders. Hence, we aim to: (1) Define the mechanisms of TDP-43 aggregation using pure components in vitro. (2) Antagonize and reverse TDP-43 aggregation with Hsp104 and p97 in vitro. (3) Prevent or reverse TDP- 43 aggregation and toxicity in vivo. These studies will provide important new mechanistic insights into TDP-43 aggregation and toxicity and how this might be antagonized. Realization of our objectives will empower the development of therapies for ALS and other TDP-43 proteinopathies. PUBLIC HEALTH RELEVANCE: Several devastating diseases that are caused by nerve degeneration, including amyotrophic lateral sclerosis (ALS), have been unified by a common underlying theme: the clumping of a protein, TDP-43, in nerve cells. Our proposed studies aim to provide new mechanistic insights into how TDP-43 clumps and is toxic, and how this process might be antagonized or reversed. Realization of our objectives will empower the development of new therapies for ALS and related disorders, which are currently untreatable.